Tubular containers having a closed-type head part designed to prevent the degradation, etc., of contents have been developed for containing food, medical products, industrial products, hair dyes, and the like.
Such tubular containers are typically of the so-called aluminum tube type and laminated tube type. With the former type, aluminum slag is introduced into a cavity and pressure is applied to the aluminum slag by inserting a mandrel into the cavity, thereby producing an aluminum tube in which the head part and body part are integrated (Patent Document 1). With the latter type, a flat laminated sheet is rounded in advance into a tubular shape, a tubular body part is formed by side seaming, and then a laminated tube is obtained by attaching a head part to the body part. A method for cutting and welding the body part in the laminated tube is described in Patent Document 2, and a compression method such as described in Patent Document 3 is an example of a method for forming a head part by attaching a head part to a body part.
Tubular containers accommodating food, medical products, industrial products, hair dyes, and the like are required to protect the contents thereof. Thus, gas-barrier ability and light-shielding ability are important due to concerns about the oxidation of the contents caused by oxygen penetration from the outside and scattering of volatile components contained in the contents to the outside. In aluminum tubes, because the body part and head part containing a closing film in the opening section are integrally molded from aluminum having a high ability to protect the contents, sufficient properties required to protect the contents are obtained.
However, in the case of a laminated tube, for example, because the material of the head part molded by the compression method is a plasticizable plastic material and because the body part and the head part are not molded integrally, the ability to protect the contents causes concerns. Thus, polyolefin resins, in particular polyethylene as a market base material, has been used as a material constituting the inner and outer layers of the body part of the laminated tube because of hot processability, chemical stability, flexibility, water resistance, utility, safety and sanitary properties, material cost thereof, etc., and polyethylene is most often used for the head part to provide for good bonding ability with the body part, and the ability of these portions to protect the contents is problematic. Furthermore, a closing film is often formed to protect the contents, but if the head part is closed with polyethylene, then it is difficult to open for use and, therefore, it becomes necessary to close the opening of the head part with another member.
From the above-described standpoints, aluminum tubes are presently used for the tubular containers accommodating medical products that require a high degree of contents protection. However, because aluminum tubes have a lower shape restoration capacity than laminated tubes, the convenience of use thereof is degraded by deformation. Furthermore, aluminum tubes are inferior to laminated tubes in terms of printing ability. For this reason, there is a strong demand for laminated tubes in the industrial circles.
Accordingly a variety of attempts have been made to improve the ability of laminated tubes to protect their contents. For example, with respect to the body part of a laminated tube, an ability to protect their contents is provided by using aluminum, an inorganic oxide vapor-deposited film, or a plastic film with a high barrier ability such as EVOH, as an interlayer of a laminated sheet. As for the head part, Patent Document 4 discloses introducing an aluminum intermediate member into the inner side of the head part, and Patent Document 5 discloses a so-called membrane tube having a cup-shaped closing member. The membrane tube is also advantageous from the standpoint of tampering prevention because it is difficult to reseal.
In a method for manufacturing the laminated tube, as shown in FIG. 8, a cup-shaped closing material 42 is produced by deep drawing from a laminate original sheet comprising an Al foil or the like as a core material, and this closing material 42 is fitted onto an engagement section 41, which is the distal end of the mandrel 40. When the closing material 42 is fitted to the mandrel 40, the inner diameter of the convex section of the closing material 42 molded in advance to have a cup-like shape is molded to be somewhat smaller than the outer diameter of the engagement section 41, which is the distal end of the mandrel 40, and the convex section of the closing material 42 is forcibly pulled on the engagement section 41 of the mandrel 40, whereby the closing material 42 is held by using the elastic force, repulsion force, dead holding ability, and frictional force of the closing material 42 on the mandrel 40, so that the closing material is prevented from falling off. A compression method is publicly known by which, after such a fitting for structural integration with the distal end of the mandrel 40 has been made, a pressure is applied to a molten resin 46 that is put in position in a cavity 45, and a closed-type head part is molded at the tubular body part, while forming the opening portion in the head part with a holepin 47.
When the contents accommodated in the closed-type container manufactured in the above-described manner is to be used, the distal end surface of the convex section of the closing material exposed in the opening portion of the head part has to be pierced with a needle-shaped object. Because the closing material has to have a high strength to withstand processing such as deep drawing, the force necessary to pierce the closing material with the needle-shaped member is larger than the joining force between the closing material and head part and a problem is associated with the closing material falling into the tubular container. Thus, the closing material is required to have the following functional properties: (i) ability to withstand deep drawing, (ii) sufficient ability to retain shape in the compression process following the deep drawing, and (iii) ability to be reliably opened with a needle-shaped member, and there is a trade-off relationship between the properties (i) and (iii).
A structure is also known in which, with the foregoing in view, the outer peripheral surface of the convex section of the closing material is embedded in the rear face of the head part in order to augment the joining force of the closing material and head part (see Patent Document 6).
With such a closing material, a protruding section is formed outwardly at the outer peripheral surface of the convex section of the closing material by deep drawing and then the closing material is mounted on the mandrel and a head part is formed by the compression method. However, a process for forming in advance the protruding section at the outer peripheral surface of the convex section of the closing material is necessary. Moreover, the distal end of the protruding section is weakened and sometimes even broken when the protruding section is mechanically molded. Yet another problem is that when the head part is formed by a compression method, the protruding section formed outwardly from the outer peripheral surface of the convex section of the closing material becomes a hindrance and the molten resin cannot properly flow around to the distal end of the head part.
Patent Document 1: Japanese Patent Publication No. 2005-161370A
Patent Document 2: Japanese Patent Publication No. 61-2489B
Patent Document 3: Japanese Patent Publication No. 64-7850B
Patent Document 4: Japanese Patent Publication No. 3-20337B
Patent Document 5: Japanese Patent Publication No. 2002-192546A
Patent Document 6: Japanese Utility Publication No. 62-69438A